*{
    padding: 0px;
    margin: 0px;
    box-sizing: border-box;
}
@keyframes rocketReadyGo {
    0%{
        background-position-x: -297px;
    }
    
    100%{
        background-position-x:-743.4px;
    }
}



body{
    height: 5000px;
    position: relative;
    overflow: scroll;
    background-image: linear-gradient(#000000,blue,green);
}
.rocket{
    width:148.6px;
    height: 249px;
    background-image: url("../img/rocket_button_up.png");
    position: fixed;
    bottom: 0px;
    cursor: pointer;
    right: 300px;
}
.rocketUping{
     /*区分好inherit (多次运动用inherit)与initial (最初的意思)*/
    animation:rocketReadyGo  steps(3) running 0.25s infinite  forwards ;
}

.rocket:hover{
    background-position-x: -149px;
}
